1. Technical Field
The present invention is related to a CMOS-MEMS cantilever structure, and particularly to a CMOS-MEMS cantilever structure using polysilicon as its piezoresistive material.
2. Description of Related Art
In the field of micro electro-mechanical systems (MEMS), cantilever beams are used in a wide variety of applications such as flow meters, biosensors, probes for atomic force microscopes, accelerometers, etc. Therefore, cantilever beams are literally one of the most frequently used structures, which are often manufactured from silicon, silicon nitride or polymer.
FIG. 1 shows a conventional MEMS cantilever device 10 manufactured by using a SOI (Silicon on Insulator) substrate 11 as its base material. The SOI substrate 11 includes a first silicon layer 13, a silicon dioxide layer 14 and a second silicon layer 15, and deposited thereon are a silicon dioxide layer 16, a piezoresistive material layer 17 and a metal layer 18. After a front-side and a back-side etching process, a cantilever beam 12 can be released from its peripheral structure to float. The cantilever beam 12 includes the second silicon layer 15, the silicon dioxide layer 14 and the piezoresistive material layer 17, and can be connected to a circuit structure through the metal layer 18.
FIG. 2 shows another conventional MEMS cantilever device 20. The MEMS cantilever device 20 mainly uses a silicon substrate 21 which is partially ion implanted to become an n-type well structure 21a. On the silicon substrate 21 and the n-type well structure 21a are deposited a silicon dioxide layer 22 and a silicon nitride layer 23, sequentially. A cantilever beam 24 as shown in FIG. 2 is formed after several etching processes.
However, the cantilever beams 12 and 24 described above suffer from shortcomings in terms of practical application. For example, relatively expensive SOI substrates are required to manufacture the cantilever beam 12, which increases costs. Furthermore, fabrication of the cantilever beams 12 and 24 involves complicated manufacturing processes which also result in higher manufacturing costs. For example, during the back-side etching process of fabrication of the cantilever beams 12 and 24, where wet etching technology is required, cleansing and drying after wet etching will increase the manufacturing time. Moreover, in order to protect the front-side structure on the MEMS cantilever devices 10 and 20, a protection device is required on the front surface before a back-side etching can be conducted, thereby increasing the complexity of operating procedures.